For openings in walls, ceilings and roofs, hereinafter referred to generally as inspection or access openings in walls, it is a common practice to frame out the opening with frame members providing an outer frame and to provide within that opening a cover which can also have a frame along its outer periphery.
These are the types of frames with which the invention is concerned and hence, in the framework of the invention, a cover frame will mean the frame adapted to be received in the inspection opening frame for the cover or closure of that opening.
Inspection and access openings can be provided practically anywhere in a structure to allow something behind that opening to be readily inspected or accessed. The opening may afford access for inspection, maintenance for control purposes to plumbing fixtures or piping, to electrical duct work or even to mechanical systems. The opening may be provided to allow access from below or above to the accessed space. In general the invention is applicable to all openings in a wall which can be provided with a cover which are to be framed out or to receive a frame and which are to be provided in any structure to accommodate an outer frame of a cover.
In inspection opening systems in the past, the frame members for the opening frame and for the cover frame generally were constituted of flat profiles, i.e. members which adjoin at mitered corners, were profiled members,i.e. extrusions or the like of a flat configuration, with a particular cross sectional shape which was selected for the aesthetic or mechanical purposes required. The profile members forming the limbs of the frame were either welded together with one another or rivetted together with the aid of flat corner members engaging in the interiors of the frame members.
The welded connection can result in an offsetting and a loss in precision of the connection of the frame members while the rivetting procedure required time-consuming efforts and additional elements, like the rivets, increasing the cost and complexity of frame assemblies.
In many instances, the method of connection did not permit assembly of the frame prior to installation or, if the frame could be assembled prior to installation, did not allow sufficient versatility for particular frame dimensions and proportions so that a wide variety of prefabricated frames was required to be stocked.